1. Technical Field
The present invention relates to a semiconductor light-emitting device such as a light-emitting diode (LED), and more particularly to a semiconductor light-emitting device having an AlGaInP-based semiconductor film.
2. Description of the Related Art
Improvements in light-emitting efficiency have expanded the applications for AlGaInP-based LEDs as light sources for display and lighting such as rear combination lamps for automobiles. The structure for an AlGaInP-based LED is summarized below. A GaAs substrate can be used as a growth substrate used for crystal growth of the semiconductor film. A buffer layer, an n-type clad layer, an active layer, a p-type clad layer are laminated or stacked on the GaAs substrate. The active layer has, for example, a quantum well structure composed of AlGaInP and InGaP, for example. The composition of the clad layer is, for example, (Al0.7Ga0.3)0.5In0.5P. The dopant can be Zn or Mg in the p-type clad layer, and Si, Te or Se in the n-type clad layer. In both cases, the Al composition of the clad layer is set so as to be higher than the active layer.
In a typical AlGaInP-type LED, a sufficient bandgap must be provided between the active layer and the clad layer in order to more effectively provide the carrier confinement effect with the clad layer. In an LED having an emission color from yellow to green, the Al composition of the clad layer has to be especially increased since the bandgap of the active layer is large.
In Japanese Laid-open Patent Publication No. 2002-353502 (referred to as Patent Document 1 hereinafter), the p-type clad layer comprises a first layer composed of In0.49(GaxAl1-x)0.51P (0≦x≦0.15) and a second layer composed of In0.49(GayAl1-y)0.51P (0.2≦y≦1), and the light-emission efficiency can be improved by setting the thickness of the first layer between 0.05 and 0.2 μm. A similar technology is disclosed in Japanese Laid-open Patent Publication No. 2004-304090 (referred to as Patent Document 2 hereinafter).